Method for preparation of a stable polymer dispersion with colloidal silica particles

Abstract

A method of preparing a polymer dispersion comprising (i) contacting an aqueous dispersion of de-ionized acidic colloidal silica particles with a first mixture of monomers to form a combination; (ii) polymerizing such combination at an initial pH of from 2 to 5 to at least 90% in completion; and (iii) adding a second mixture of monomers at a rate substantially equal to the rate of consumption of such second mixture of monomers to continue and complete the polymerization. The present invention further provides a polymer dispersion made from the above method.

What is claimed is: 
     
       1. A coating composition comprising a polymer dispersion, the polymer dispersion comprising, (a) a polymer formed by polymerizing monomers, the amount of the monomers being from 30% to 90% by dry weight based on total dry weight of the polymer dispersion, and (b) de-ionized acidic colloidal silica particles in an amount of from 10% to 70% by dry weight based on total dry weight of the polymer dispersion,
 wherein the viscosity stability (ΔKU) of the coating composition as determined by Stormer viscometer according to ASTM D562 method is from 5 to 9. 
 
     
     
       2. The coating composition of  claim 1 , wherein the polymer dispersion comprises from 20% to 50% of de-ionized acidic colloidal silica particles. 
     
     
       3. A coating composition comprising a polymer dispersion, wherein the polymer dispersion is prepared by a method comprising
 (i) contacting an aqueous dispersion of de-ionized acidic colloidal silica particles with a first mixture of monomers to form a combination, wherein the de-ionized acidic colloidal silica particles are present in an amount of 10% to 70% be dry weight based on total dry weight of the polymer dispersion; 
 (ii) polymerizing said combination at an initial pH of from 2 to 5 to at least 90% in completion; and 
 (iii) adding a second mixture of monomers at a rate substantially equal to the rate of consumption of said second mixture of monomers to continue and complete the polymerization, wherein the viscosity stability (ΔKU) of the coating composition as determined by Stormer viscometer according to ASTM D562 method is from 5 to 9. 
 
     
     
       4. The coating composition of  claim 3 , wherein a total amount of the first and the second mixtures of monomers is from 30% to 90% by dry weight based on total dry weight of the polymer dispersion. 
     
     
       5. The coating composition of  claim 3 , wherein the amount of the first mixture of monomers is from 1% to 30% by dry weight based on total dry weight of the first and the second mixtures of monomers. 
     
     
       6. The coating composition of  claim 1 , wherein the de-ionized acidic colloidal silica particles have an average diameter of from 2 nm to 150 nm. 
     
     
       7. The coating composition of  claim 3 , wherein at least one of the first and the second mixtures of monomers is selected from acrylic or methacrylic ester monomers, acrylonitrile or methacrylonitrile, styrene or substituted styrene, butadiene, ethylene, propylene, a-olefin, vinyl ester, and any combination thereof. 
     
     
       8. The coating composition of  claim 3 , at least one of the first and the second mixtures of monomers further comprise from 0.1% to 10% by dry weight based on total dry weight of the monomers, of an ethylenically unsaturated monomer carrying at least one functional group selected from carboxyl, carboxylic anhydride, hydroxyl, amide, amino, ureido, acetoacetate, sulphonate, phosphonate and any combination thereof. 
     
     
       9. The coating composition of  claim 3 , wherein at least one of the first and the second mixtures of monomers further comprise, from 0.1% to 5% by dry weight based on total dry weight of the monomers, of a surfactant. 
     
     
       10. The coating composition of  claim 1 , wherein the de-ionized acidic colloidal silica particles are made from precipitated silica, micro silica, pyrogenic silica, or any combination thereof. 
     
     
       11. The coating composition of  claim 3 , wherein the de-ionized acidic colloidal silica particles have an average diameter of from 2 nm to 150 nm. 
     
     
       12. The coating composition of  claim 3 , wherein the de-ionized acidic colloidal silica particles are made from precipitated silica, micro silica, pyrogenic silica, or any combination thereof. 
     
     
       13. The coating composition of  claim 3 , wherein the polymer dispersion comprises from 20% to 50% of de-ionized acidic colloidal silica particles. 
     
     
       14. The coating composition of  claim 1  wherein the monomers comprise polymerizable ethylenically unsaturated monomers.